The invention relates to new polyethers, their preparation and their use as lubricants, in particular as lubricants for power-transmission gears.
Power-transmission gears should operate with as little loss as possible in order to achieve a good transmission efficiency and to maintain a low level of heating of the gear units.
The total losses occurring in a gear unit comprise the frictional losses, which arise from the transmission of motion, under high contact force, by the surfaces which are rolling and simultaneously sliding on one another, and the churning losses and compression losses which are caused by the immersion of moving machine parts into the oil charge [Eiselt, H.: Beitrag zur experimentellen und rechnerischen Bestimmung der Fresstragfahigkeit von Zahnradgetriben unter Berucksichtigung der Zahnflankenreibung (Contribution on the experimental and theoretical determination of the load-carrying capacity, without seizing, of toothed gears, taking into account toothflank friction), Thesis, TU Dresden 1966; Ohlendorf, H.: Verlustleistung und Erwarmung von Stirnradern (Power losses and heating of spur wheels), VDI-Z. 102 (1960) 216 bis 224; Huber G.: Untersuchungen uber Flankentragfahigkeit und Wirkungsgrad von Zylinderschneckengetrieben (Evolventenschnecken) (Investigations on flank load-carrying capacity and efficiency of cylindrical worm-gears (involute worm-gears)), Thesis, TU Munich1978]. The compression losses are substantial, particularly in the case of high speed gears.
The lubricants employed in power-transmission gears which have a positive transmission of motion serve to minimize the frictional losses between the surfaces. At the same time, a stable lubricating film, which builds up owing to the rolling motion of the surfaces, should separate these surfaces from one another in order to keep wear of all types (seizing wear, pitting wear, low-speed wear and grey-spot wear) as low as possible.
The lubricant should have a minimum viscosity in order to be able to build up a sufficiently stable lubricating film. The more unfavourable the operating conditions, the greater must the chosen viscosity be in order to avoid unreliable wear. On the other hand, however, the churning losses increase sharply with increasing viscosity, resulting in an increase in the temperature of the gear unit.
Depending on the function of the lubricant in a power-transmisson gear, the lubricating qualities of liquid lubricants are determined by the frictional behavior under the operating conditions (Winter, H. and Vojacek, Influence of the Molecular Structure on the Traction Characteristics of Lubrication Fluids. Int. Symp. on Gearing Power Transm., Tokyo 1981), by the viscosity at the operating temperature, by the viscosity/temperature characteristics and by the viscosity/pressure coefficient .alpha. which influences the thickness of the lubricating film (Schmiertechnik und Tribologie 27 (1980) 55 bis 57).
The frictional behavior is determined by the friction coefficient. It is defined as the quotient of the frictional force, due to the friction, and the contact force between the surfaces.
The friction coefficient essentially depends on the operation parameters, peripheral velocity of the surfaces which roll and slide on one another, slip and contact force between the two surfaces, the slip being defined as the absolute value of the quotient of the difference in the two peripheral velocities and the greater peripheral velocity.
The friction coefficient should be as low as possible in all operating areas in order to keep the frictional losses at a low level.
The viscosity of the lubricant should be as low as possible, the minimum viscosity at the operating temperature depending on the operating conditions.
The viscosity should depend as little as possible on the temperature. The viscosity index (generally abbreviated as VI) serves as a measure of the temperature dependence of the viscosity. The viscosity index should be as high as possible.
In addition, the lubricants should be compatible with the mineral oils customarily used in the systems to be lubricated (for example mechanical gears, roller bearings and plain bearings) so that complications do not arise with the residual amounts of mineral oils when a change is made from the mineral oils to the new lubricants. They should also be as hydrophobic as possible, since absorbed water promotes corrosion. In addition, a high thermal load capacity is desirable.
Japanese Preliminary Published Specification 50/13 3205 discloses polyalkylene glycol ethers which contain C.sub.8 -C.sub.28 1,2-epoxyalkane units and have a ratio of carbon to oxygen of from 3.5 to 9.5. Although these known polyalkylene glycol ethers can be used as lubricants in mixtures with mineral oils, their lubricating properties are not completely satisfactory in every respect. This becomes evident from the excessive coefficients of shearing friction.
The polyalkylene alkylene oxides disclosed in U.S. Pat. No. 3,382,055, which can be used as additives for relatively light lubricating oils, also have excessive friction coefficients.